Immunoblot of clonal β-cell fractions separated by differential centrifugation. INS1 (A) or MIN6 (B) cell fractions (20 μg per lane) were probed with rabbit anti-PMR1 (1:1,000) or, in A, with rabbit anti-mitochondrial glycerol phosphate dehydrogenase (mGPDH; 1:500; mitochondrial marker) or mouse anti-RyR II
(1:1,000; ER marker). Immunoreactivity was visualized with anti-rabbit IgG HRP (1:80,000; Sigma) or anti-mouse IgG HRP (1:10,000;
Sigma). INS1 fraction insulin content was measured by radioimmunoassay. Results shown are representative of three separate
experiments performed for each cell type.